This application claims the priority benefit of Taiwan application serial no. 89118783, filed Sep. 14, 2000.
1. Field of the Invention
The invention relates in general to a method and an apparatus for automatically correcting a projection display of a projector. More particularly, this invention relates to a method and an apparatus for automatically correcting a projection display of a projector.
2. Description of the Related Art
With the projection lens as a reference, when the projection lens is located horizontally, an image projected perpendicularly to the projection lens has a standard projection angle. With such a standard projection angle, the image projected on the screen typically has a rectangular frame. If the projection lens is shifted higher, lower or oblique from the horizontal, that is, when the image projected from the projector is not perpendicular to the projection lens, this rectangular frame is then distorted, normally as a trapezium frame.
In a convention projector with the design of trapezium distortion correction, a trapezium distortion correction software is used to drive an electronic circuit after adjusting the projection angle. A correction image is then generated. As the adjustment of the projection angle is distinguished by human eyes, whether the optimum correction of image distortion is obtained cannot precisely tell. In addition, for non-professional users, the direction of adjustment is always confusing. Therefore, it is difficult to precisely and properly adjust.
The invention provides a method and an apparatus for automatically correcting a projection display of a projector. The disposition parameters such as the distance between a disposition surface for disposing the projector and a projection axis of the projector, the horizontal inclination angle or vertical inclination angle for the projector can be monitored in real time. From the parameters and an accompanied circuit, the distortion frame can be automatically corrected without being distinguished by a user. When the projector has been shifted during operation, the distorted framed can be corrected via a software. The user does not need to monitor whether there is a distortion or whether the projector is moved all the time.
In the method provided by the invention, disposition parameters of a projector are detected by a detector built in the projector. The disposition parameters include the disposition distance, the horizontal inclination angle between the projection axis and the disposition surface, and the vertical inclination angle between a line normal to the projection axis and a line normal to the disposition surface. Whether any of the disposition parameters deviates from its corresponding standard reference value with which there no distortion occurs is determined by the control circuit. A trapezium correction value according to a deviation of any of the disposition parameters is obtained when the disposition parameter deviates from its standard reference value. An input image signal is corrected with the trapezium correction value.
The apparatus for automatically correcting the projection display of a projector comprises a detector and a control circuit. The detector detects the disposition parameters of the projector in a real time. The control circuit receives the disposition parameters and corrects an input image signal with a trapezium correction value obtained according to a deviation between the disposition parameters and standard reference values of the disposition parameters.
The detector further comprises a disposition distance detector installed in the projector to detect the disposition distance and the vertical inclination angle. Alternatively, the detector comprises an inclination angle detector to detect both the vertical and horizontal inclination angles. In addition, a video signal decoder is include to receive and decode an input video signal. An input frame buffer is to receive and temporarily store the video signal decoded by the video signal decoder. A look up table is to provide a trapezium correction value according to the disposition parameters. An output frame buffer is to receive the corrected video signal from the control circuit and to project an image on a screen according to the corrected video signal via an optical system.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.